Pipe used for underground work is typically provided with a flared bell at one end and a spigot at the opposite end. The flared bell end is formed with a predetermined inner diameter, which defines a first sliding surface. The spigot end is formed with a predetermined outer diameter, which defines a second sliding surface. The inner diameter of the flared bell end is greater than the outer diameter of the spigot end. This allows lengths of pipe to be joined end-to-end by inserting the spigot end of one pipe into the flared bell end of another pipe. However, since the inner diameter of the flared bell is greater than the outer diameter of the spigot, an annular space is created therebetween. The annular space must be sealed by a suitable means in order to prevent fluid leakage where the pipes are connected together.
Two known means for sealing such annular spaces include the use of a rolling type ring seal or a sliding type ring seal. In a conventional sliding type ring seal, the seal is first placed on the sealing surface of the spigot at one end of a pipe. The spigot is inserted into the flared bell end of another pipe. As the spigot is inserted, a surface of the seal engages and slides back against the sealing surface of the flared bell end. This distorts the original shape of the ring seal resulting in the annular space between the two sealing surfaces being closed. However, as the sealing surface of the flared bell end engages and distorts the seal, frictional forces are generated. In order to reduce these frictional forces at the point in which the sliding takes place, it is desirable to apply a lubricant to the ring seal.
An example of sliding type ring seal having a lubricant applied to the seal is illustrated in U.S. Pat. No. 4,934,716. An annular seal is positioned on a shoulder of a spigot at one end of a length of pipe. The seal is comprised of two portions, namely, a main body and a flexible lip. The lip is connected with the main body at the base thereof, and extends up the entire height of the main body. The main body and the lip are provided with opposed surfaces which constitute the sliding surfaces of the seal. A pocket is formed by the opposed surfaces. A lubricant is located in the pocket to facilitate sliding between the surfaces of the seal when the spigot is inserted into a bell end of another pipe.